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Navien E016 — Heat Exchanger Overheating
Your Navien shut down because the heat exchanger ran past its safe temperature limit — almost always a scale or water-flow problem, not a gas problem.
What E016 Means
The E016 lockout means the temperature inside the heat exchanger climbed past the point Navien considers safe. When water can't carry heat away from the exchanger fast enough, the metal temperature spikes and the unit shuts itself down to protect the heat exchanger from damage.
The good news: E016 is almost never a combustion or gas fault. It's a flow-and-scale story. The fix is usually restoring proper water flow and descaling the heat exchanger — routine maintenance that also keeps the code from coming back.
Common Causes of E016
1. Scale buildup in the heat exchanger
Hard water leaves mineral scale that insulates the heat exchanger and chokes flow. The most common root cause on units that have never been descaled. A flush usually clears it.
2. Restricted or low water flow
A partially closed valve, low incoming pressure, or a clogged fixture can drop flow below what the unit needs to shed heat, tripping the over-temp limit.
3. Clogged cold-water inlet filter
Navien units have an inlet screen that traps debris. When it clogs, flow through the exchanger drops and temperatures climb. A quick clean often resolves it.
4. Failed high-limit sensor
Less common, but a faulty over-temperature sensor can report a false high reading. We verify the sensor before condemning anything expensive.
E016 FAQs
Why South Shore homeowners choose Johnson Bros.
Navien showing E016? Usually a descale and a flow check.
Tell us your model number and how long the code has been showing. Most E016s are maintenance, not major parts.
Need help fast? Call for urgent plumbing issues. Booking online is best when you want the next open appointment without waiting on the phone.
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Navien showing E016? Usually a descale and a flow check.
Tell us your model number and how long the code has been showing. Most E016s are maintenance, not major parts.
Call for urgent help now. Book online when you want the next available fit for your schedule.